Ed25519 and Ed448 Public Key Algorithms for the Secure Shell (SSH) Protocol2A Eachard RoadCambridgeCB3 0HYUnited Kingdombjh21@bjh21.me.ukcyberstorm.mu88, Avenue De PlevitzRoches BrunesMauritiuslogan@cyberstorm.mucurdle
This document describes the use of the Ed25519 and Ed448 digital
signature algorithms in the Secure Shell (SSH) protocol. Accordingly,
this RFC updates RFC 4253.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
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Table of Contents
. Introduction
. Conventions Used in This Document
. Requirements Language
. Public Key Algorithm
. Public Key Format
. Signature Algorithm
. Signature Format
. Verification Algorithm
. SSHFP DNS Resource Records
. IANA Considerations
. Security Considerations
. References
. Normative References
. Informative References
Acknowledgements
Authors' Addresses
Introduction
Secure Shell (SSH) is a secure
remote-login protocol. It provides for an extensible variety of
public key algorithms for identifying servers and users to one
another. Ed25519 is a digital
signature system. OpenSSH 6.5
introduced support for using Ed25519 for server and user
authentication and was then followed by other SSH implementations.
This document describes the method implemented by OpenSSH and others
and formalizes the use of the name "ssh-ed25519". Additionally,
this document describes the use of Ed448 and formalizes the use of the
name "ssh-ed448".
Conventions Used in This Document
The descriptions of key and signature formats use the notation
introduced in and the string data type from .
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
Public Key Algorithm
This document describes a public key algorithm for use with SSH,
as per . The name of the algorithm is "ssh-ed25519". This
algorithm only supports signing and not encryption.
Additionally, this document describes another public key algorithm.
The name of the algorithm is "ssh-ed448". This algorithm only supports
signing and not encryption.
Standard implementations of SSH SHOULD implement these signature algorithms.
Public Key Format
The "ssh-ed25519" key format has the following encoding:
string
"ssh-ed25519"
string
key
Here, 'key' is the 32-octet public key described in
.
The "ssh-ed448" key format has the following encoding:
string
"ssh-ed448"
string
key
Here, 'key' is the 57-octet public key described in
.
Signature Algorithm
Signatures are generated according to the procedure in Sections
and of .
Signature Format
The "ssh-ed25519" key format has the following encoding:
string
"ssh-ed25519"
string
signature
Here, 'signature' is the 64-octet signature produced in
accordance with .
The "ssh-ed448" key format has the following encoding:
string
"ssh-ed448"
string
signature
Here, 'signature' is the 114-octet signature produced in
accordance with .
Verification Algorithm
Ed25519 signatures are verified according to the procedure in
.
Ed448 signatures are verified according to the procedure in
.
SSHFP DNS Resource Records
Usage and generation of the SSHFP DNS resource record
is described in .
The generation of SSHFP resource records for "ssh-ed25519" keys is described
in .
This section illustrates the generation of SSHFP resource records for "ssh-ed448" keys, and
this document also specifies the corresponding Ed448 code point to "SSHFP RR
Types for public key algorithms" in the "DNS SSHFP Resource Record Parameters"
IANA registry .
The generation of SSHFP resource records for "ssh-ed448" keys
is described as follows.
The encoding of Ed448 public keys is described in . In brief,
an Ed448 public key is a 57-octet value representing a 455-bit y-coordinate
of an elliptic curve point, and a sign bit indicating the corresponding
x-coordinate.
The SSHFP Resource Record for the Ed448 public key with SHA-256 fingerprint
would, for example, be:
example.com. IN SSHFP 6 2 ( a87f1b687ac0e57d2a081a2f2826723
34d90ed316d2b818ca9580ea384d924
01 )
The '2' here indicates SHA-256 .
IANA Considerations This document augments the Public Key Algorithm Names in .
IANA has added the following entry to "Public Key Algorithm Names" in the
"Secure Shell (SSH) Protocol Parameters"
registry :
Public Key Algorithm Name
Reference
ssh-ed25519
RFC 8709
ssh-ed448
RFC 8709
IANA has added the following entry to "SSHFP RR Types for public
key algorithms" in the "DNS SSHFP Resource Record Parameters" registry
:
Value
Description
Reference
6
Ed448
RFC 8709
Security Considerations
The security considerations in apply to all SSH
implementations, including those using Ed25519 and Ed448.
The security considerations in and apply to all uses of
Ed25519 and Ed448, including those in SSH.
ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.The Secure Shell (SSH) Protocol Assigned NumbersThis document defines the instructions to the IANA and the initial state of the IANA assigned numbers for the Secure Shell (SSH) protocol. It is intended only for the initialization of the IANA registries referenced in the set of SSH documents. [STANDARDS-TRACK]The Secure Shell (SSH) Protocol ArchitectureThe Secure Shell (SSH) Protocol is a protocol for secure remote login and other secure network services over an insecure network. This document describes the architecture of the SSH protocol, as well as the notation and terminology used in SSH protocol documents. It also discusses the SSH algorithm naming system that allows local extensions. The SSH protocol consists of three major components: The Transport Layer Protocol provides server authentication, confidentiality, and integrity with perfect forward secrecy. The User Authentication Protocol authenticates the client to the server. The Connection Protocol multiplexes the encrypted tunnel into several logical channels. Details of these protocols are described in separate documents. [STANDARDS-TRACK]The Secure Shell (SSH) Transport Layer ProtocolThe Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network.This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression.Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated.This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. [STANDARDS-TRACK]Using DNS to Securely Publish Secure Shell (SSH) Key FingerprintsThis document describes a method of verifying Secure Shell (SSH) host keys using Domain Name System Security (DNSSEC). The document defines a new DNS resource record that contains a standard SSH key fingerprint. [STANDARDS-TRACK]Use of the SHA-256 Algorithm with RSA, Digital Signature Algorithm (DSA), and Elliptic Curve DSA (ECDSA) in SSHFP Resource RecordsThis document updates the IANA registries in RFC 4255, which defines SSHFP, a DNS Resource Record (RR) that contains a standard Secure Shell (SSH) key fingerprint used to verify SSH host keys using DNS Security Extensions (DNSSEC). This document defines additional options supporting SSH public keys applying the Elliptic Curve Digital Signature Algorithm (ECDSA) and the implementation of fingerprints computed using the SHA-256 message digest algorithm in SSHFP Resource Records. [STANDARDS-TRACK]Edwards-Curve Digital Signature Algorithm (EdDSA)This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Informative ReferencesEd448-Goldilocks, a new elliptic curveSecure Shell (SSH) Protocol ParametersIANADNS SSHFP Resource Record ParametersIANAOpenSSH 6.5 release notesUsing Ed25519 in SSHFP Resource RecordsThe Ed25519 signature algorithm has been implemented in OpenSSH. This document updates the IANA "SSHFP RR Types for public key algorithms" registry by adding an algorithm number for Ed25519.Acknowledgements
The OpenSSH implementation of Ed25519 in SSH was written by
. We are also grateful to , , and
for their comments.
Authors' Addresses2A Eachard RoadCambridgeCB3 0HYUnited Kingdombjh21@bjh21.me.ukcyberstorm.mu88, Avenue De PlevitzRoches BrunesMauritiuslogan@cyberstorm.mu